Electric induction heat treatment of an end of tubular material

ABSTRACT

A magnetic flux concentrator is used to control the end heating of a tubular material in an electric induction heat treatment process. The magnetic flux concentrator may consist of fixed elements, or a combination of fixed and moveable elements to accommodate end heating of tubular materials having different dimensions or material properties.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of application Ser. No. 11/691,751, filed Mar. 27, 2007, which application claims the benefit of U.S. Provisional Application No. 60/794,492, filed Apr. 24, 2006, both of which applications are hereby incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to electric induction heat treatment of the end regions of a tubular material.

BACKGROUND OF THE INVENTION

Electric induction heating can be used to heat treat tubular materials such as metal tubes and pipes. Typically the tubular material is held in place within a solenoidal induction coil as illustrated in FIG. 1. Tube 90 is placed within solenoidal coil 30. When suitable ac power is applied to the coil, the tube is inductively heated by magnetic coupling with the longitudinal flux field established by the flow of ac current through the coil. The heat treatment may be, for example, annealing, normalizing, stress relieving, coating, drying, hardening or tempering of the end of the tubular material. In other applications induction end heating of tubular products can be used for heating ends prior to metal forming operations. Some applications require uniform heating of a specific length of an end portion of the tubular material.

As shown in FIG. 1, when uniform end heat treatment is desired, the tubular material is situated in the coil so that the coil “overhangs” the end of the material. Generally the longitudinal axis, X, of the coil and tubular material are coincident and the solenoidal coil is shaped to coincide with the shape of the tubular material. The overhang distance, x_(oh), controls the shape of the flux field established at an axial end of the coil beyond the end of the tubular material so that the flux field intensity is established within the end of the material to uniformly heat it to the required length. The proper overhang distance is affected by a number of parameters, including the outside diameter of the tubular material, the material's thickness, physical and metallurgical properties, and the frequency of the ac power applied to the coil. Therefore different coils are required for tubular materials of different sizes, or for heat treating the same tubular material to different end lengths. Compare, for example, FIG. 2( a), FIG. 2( b) and FIG. 2( c) wherein the same induction coil 30 and overhang distance, x_(oh), is used to induction heat an end of: (1) tubular material 90 a having an outside diameter (OD) equal to OD₁ and thickness t₁; (2) tubular material 90 b having an outside diameter OD₂, which is smaller than OD₁, and thickness t₁; and (3) tubular material 90 c having an outside diameter OD₂ and thickness t₂, which is greater than t₁, respectively. As illustrated by the graphs in FIG. 2( d), for tubular material 90 a in FIG. 2( a), required end heated length 92, thermal transition zone 94 and cold zone 96 all vary. The term “required end heated length” typically refers to a uniform heating temperature distribution over the required end heated length. Since heat cannot be induced in an end length of the material with an abrupt transition to a “no heat” (or cold) end zone, there is an end length with a thermal transition zone 94 wherein the heat decreases gradually towards the cold zone 96 due to a “soaking” effect whereby heat induced in the required end heated length conducts from the required end heated length 92 towards the cold zone 96. Control of both the required end heated length and the length of the thermal transition zone is important in some heat treatment processes. For tubular materials 90 b and 90 c in FIG. 2( b) and FIG. 2( c), respectively, due to the electromagnetic end effect that exists at the coil end, the materials are not sufficiently heated along the full length of required end heated length 92′ and 92″, respectively. At the end of the tube there is under-heated zone 91. When it is necessary to heat a tubular material with a smaller OD using a coil designed for a larger OD, the end of the tube will be under-heated (zone 91) due to the reduction of heat sources caused by the electromagnetic end effect. If the tubular material is of the same shape, but fabricated from a material having different physical or metallurgical properties, for example a metal that has higher electrical resistivity, then the end of the tube will also be under-heated due to the reduction of heat sources caused by the electromagnetic end effect.

Alternatively a single coil with multiple taps of ac power connections along the length of the coil would allow some additional flexibility for uniform tubular end heating of tubular materials of different dimensions or metallurgical composition. By using appropriate taps for ac power connection, the energized length of the coil can be changed to adjust the overhang distance. Unfortunately, there is a limitation in using coil overhang for obtaining a uniform end heating. This limitation is particularly noticeable when heating magnetic metals below Curie temperature. After reaching certain values, a further increase in coil overhang will not compensate for the lack of heat sources caused by the electromagnetic end effect. In addition, large coil overhangs result in a reduction in coil efficiency and coil power factor. Both factors negatively affect cost effectiveness and flexibility of an induction system due to higher energy losses and the necessity to use special means for coil power factor correction.

One object of the present invention is to improve the end temperature heating uniformity of various types of tubular materials in an electric induction heat treatment process wherein at least one end region of the tubular material is inserted into a solenoidal induction coil. Another object of the present invention is improving flexibility of the induction heating system to permit required (for example, uniform) heating of tubular products of different geometries and materials using the same induction heater.

BRIEF SUMMARY OF THE INVENTION

In one aspect the present invention is an apparatus and method of electric induction heating of the end regions of a tubular material. At least one end region of the tubular material is inserted into an induction coil that is supplied with ac power to establish an ac magnetic field that couples with the tubular material to inductively heat it. In some examples of the invention, the end of tube flux concentrator comprises a base, a plurality of peripheral poles extending around the peripheral regions of a tube-facing side of the base, and at least one central pole extending generally from the central region of the tube-facing side of the base. The longitudinal axis of the flux concentrator passes through, and is generally perpendicular to, the tube-facing side of the base. The at least one central pole protrudes at least partially into the overhang region of the induction coil that is adjacent to the end of the tube, and the plurality of peripheral poles extend at least partially around the exterior of the end of the induction coil. In other examples of the invention, the flux concentrator can include a leg located adjacent to the extended end of at least one of the plurality of peripheral poles. The leg is optionally moveable in a direction generally parallel to the length of the at least one of the plurality of peripheral poles. In other examples of the invention, the base does not protrude into the end of the induction coil.

In another aspect the present invention is an apparatus and method of electric Induction heating of the end regions of a tubular material. At least one end of the tubular material is inserted into an induction coil that is supplied with ac power to establish an ac magnetic field that couples with the tubular material to inductively heat it. In some examples of the invention, an end of tube flux concentrator comprises a base, central pole and a plurality of peripheral poles. In some examples of the invention, the central pole protrudes at least into the overhang region of the induction coil that is adjacent to the end of the tube, and the plurality of peripheral poles extend at least partially around the exterior of the end of the induction coil. In other examples of invention, the flux concentrator can include a leg located adjacent to the extended end of at least one of the plurality of peripheral poles. The leg is optionally moveable in a direction generally parallel to the longitudinal axis of the flux concentrator.

The above and other aspects of the invention are further set forth in this specification and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings, as briefly summarized below, are provided for exemplary understanding of the invention, and do not limit the invention as further set forth in this specification and the appended claims:

FIG. 1 illustrates in a cross sectional diagram a prior art apparatus for electric induction heat treatment of a tubular material.

FIG. 2( a), FIG. 2( b) and FIG. 2( c) illustrate in cross sectional diagrams, prior art apparatus for electric induction heat treatment of tubular materials having different dimensions.

FIG. 2( d) graphically compares induced end heating of tubular materials shown in FIG. 2( a), FIG. 2( b) and FIG. 2( c).

FIG. 3 illustrates in a cross sectional diagram one example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 4( a) and FIG. 4( b) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 5( a) and FIG. 5( b) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 6( a) and FIG. 6( b) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 7( a), FIG. 7( b) and FIG. 7( c) illustrate in an end elevational view alternative examples of the magnetic flux concentrator illustrated in FIG. 3 with varying number of peripheral poles.

FIG. 8( a) is a perspective view of the magnetic flux concentrator illustrated in FIG. 7( a).

FIG. 8( b) is a perspective view of a magnetic flux concentrator with a conical central section used for electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 9( a) and FIG. 9( b) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 10( a), FIG. 10( b) and FIG. 10( c) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 11( a) illustrates in cross sectional diagram another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 11( b) is an end elevational view of one example of an adjustable iris diaphragm used with some examples of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 12 is a perspective view of another magnetic flux concentrator used for electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 13( a) and FIG. 13( b) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 14( a) and FIG. 14( b) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 15( a) and FIG. 15( b) illustrate in cross sectional diagrams another example of the electric induction heat treatment of an end of a tubular material of the present invention.

FIG. 16( a), FIG. 16( b) and FIG. 16( c) illustrate in an end elevational view alternative examples of the magnetic flux concentrator illustrated in FIG. 12 with varying number of peripheral poles.

FIG. 17( a), FIG. 17( b) and FIG. 17( c) illustrate another example of the electric induction heat treatment of an end of a tubular material of the present invention wherein the magnetic flux concentrator has elements radially adjustable along the central axis of the tubular material.

FIG. 18( a), FIG. 18( b) and FIG. 18( c) illustrate repositioning of the adjustable elements of the magnetic flux concentrator illustrated in FIG. 17( a), FIG. 17( b) and FIG. 17( c).

FIG. 19 illustrates one example of the electric induction heat treatment of an end of a tubular material of the present invention wherein an induction coil with variable turns ratio is used.

DETAILED DESCRIPTION OF THE INVENTION

One non-limiting example of the electric induction heat treatment apparatus for end heating of a tubular material of the present invention is illustrated in FIG. 3. End of tube magnetic flux concentrator 10 comprises base 10 a having a plurality of peripheral poles 10 b and a central pole 10 c extending from a surface of the base generally in the axial direction of tubular material 95, which is inserted into induction coil 30 for induction heat treatment when ac power is applied to the coil. The central pole is located interior to the inside diameter of the tubular material. The peripheral poles are located around the peripheral regions of the base and are external to the exterior surface of the tubular material and the induction coil as shown in the FIG. 3. Concentrator 10 can be moved either in the +X or −X direction to accommodate tubular materials of different dimensions, or to affect the end lengths of heat treatment. Changing the position of concentrator 10 relative to the fixed position of coil 30 and tubular material 95 results in controlled end heating of tubular material of different sizes, lengths or metallurgical properties within the same coil.

For example, FIG. 4( a) and FIG. 4( b) illustrate the use of the same magnetic flux concentrator 10 to heat two tubular materials having different inside diameters and wall thicknesses, namely tubular material 95 a in FIG. 4( a), which has a smaller inside diameter and greater thickness than tubular element 95 b in FIG. 4( b). In FIG. 4( a) the end of central pole 10 c of concentrator 10 is positioned along the X-axis in the interior opening of the tubular element 95 a for a distance x₁ to achieve required end heated length 92; whereas in FIG. 4( b) central pole 10 c of concentrator 10 is positioned along the X-axis into the interior opening of tubular element 95 b for a distance x₂ to achieve required end heated length 92. Depending upon specific requirements of an application, the distance x₂ could be negative (X-position of the end of the tubular material establishing x=0 as indicated in FIG. 4( b)); that is, the end 10 c _(end) of the central pole 10 c can be located at a certain distance outside of the tube in the coil overhang region.

FIG. 5( a) and FIG. 5( b) illustrate another non-limiting example of the present invention. In these examples of the invention, concentrator 11 comprises base element 11 a, a plurality of peripheral poles 11 b and central pole 11 c. Additionally the base and peripheral poles are fixed in position, along with solenoidal coil 30 and tubular material 95 c or 95 d. The base and peripheral poles surround at least a part of the longitudinal length of coil 30. Optionally leg element 11 d may be provided for one or more of the peripheral poles. In this example, leg element 11 d is located at the extended end of each peripheral pole and faces the exterior of the tubular material. Central pole 11 c can move in the +X and −X directions along the X-axis. As illustrated in FIG. 5( a) the end of central pole 11 c is positioned along the X-axis into the interior opening of tubular element 95 c for a distance of x₃ to achieve required end heated length 92; whereas in FIG. 5( b) central pole 11 c of concentrator 11 is positioned along the X-axis into the interior opening of tubular element 95 d for a distance X₄ to achieve required end heated length 92. Depending upon specific requirements of an application, the distance X₄ could be negative; that is, the end 11 c _(end) of the central pole 11 c can be located at a certain distance outside of the tube in the coil overhang region.

FIG. 6( a) and FIG. 6( b) illustrate another non-limiting example of the present invention. These examples are similar to those in FIG. 5( a) and FIG. 5( b) except that leg element 11 d is moveable in a direction generally parallel to the length of the adjacent peripheral pole element. This example of the present invention is particularly useful in controlling the thermal transition length 94. As illustrated in FIG. 6( a), leg element 11 d is positioned along the peripheral pole element at a distance of x′₅ from the extended end of the peripheral pole element to achieve required end heated length 92; whereas in FIG. 6( b), leg element 11 d is positioned at x′₀, which is defined as the end of the peripheral pole element. In other examples of the invention, a combination of movement of leg element 11 d and central pole 11 c, as described above, may be used.

In other non-limiting examples of the invention, any of the flux concentrators may be an “E”-shaped concentrator comprising a pair of peripheral poles as illustrated in FIG. 7( a) and FIG. 8( a) or FIG. 8( b). In other examples of the invention, the number of peripheral poles may be increased, for example, to four or six, as shown in FIG. 7( b) and FIG. 7( c), respectively, or any other number of poles. Although the peripheral poles are illustrated as curved rectangular elements in FIG. 8( a) and FIG. 8( b), they may be of different shapes, as long as they establish a magnetic field around the end of the tubular material inside the induction coil. As a limitation, the number of poles may increase to the point that the peripheral poles generate into a solid cylindrical peripheral pole structure around the base element of the concentrator. Although the base elements of the above flux concentrators are illustrated as circular disks in FIG. 7( a) through FIG. 7( c), FIG. 8( a) and FIG. 8( b), they may be of other shapes depending upon the particular tubular material to be inductively heat treated. Although the central pole is illustrated as a single cylindrical element in some of the above examples of the invention, the central pole may be of different shapes, for example, conical as shown in FIG. 8( b), and may consist of multiple central pole elements that establish a composite magnetic field around the end of the tubular material.

FIG. 9( a) and FIG. 9( b) illustrate examples of the present invention that are particularly suited for use with low resistivity tubular material (for example, copper, brass or aluminum compositions). In the example of FIG. 9( a), a central pole element is not used. Concentrator 13 comprises base element 13 a, and a plurality of peripheral poles 13 b, each of which has an optional leg element 13 d, located adjacent to its extended end. Base element 13 a is an annulus in this non-limiting example of the invention. Alternatively base element 13 a may be an adjustable iris diaphragm with an adjustable opening or aperture as illustrated in FIG. 11( b). The base, peripheral poles and legs are fixed in position, along with solenoidal coil 30 and tubular material 95 g. The base, peripheral poles and legs surround at least a part of the longitudinal length of coil 30. The end of tubular material 95 g is flush with the facing surface of base element 13 a, and consequently, there is no overhang distance. Although FIG. 9( a) and FIG. 9( b) show the end of tubular material 95 g and 95 h, respectively, flush with base element 13 a and 13 a′, respectively, of the flux concentrator, in other examples of the invention, the end of the tube may be offset from the surface of the base, and the diameter, d₁, of the annulus hole may be smaller that the inner diameter of the tubular material inside the induction coil. The arrangement shown in FIG. 9( b) is similar to the arrangement in FIG. 9( a) except that base element 13 a′ of concentrator 13′ is a solid cylindrical disk.

FIG. 10( a), FIG. 10( b) and FIG. 10( c) illustrate examples of the present invention that are particularly suited for use with high resistivity tubular material (for example, graphite or electrically conductive ceramic compositions). In the example of FIG. 10( a), a central pole element is not used. Concentrator 14 comprises base element 14 a, and a plurality of peripheral poles 14 b, each of which has an optional leg element 14 d located adjacent to its extended end. Base element 14 a is an annulus in this non-limiting example of the invention and has annular offset element 14 e extending around its opening on the tube-facing side of the base element to extend the base element into the overhang region. All elements of concentrator 14 are fixed in position, along with solenoidal coil 30 and tubular material 95 j, during the heating process. The end of tubular material 95 j is flush with the facing surface of annular offset element 14 e. The arrangement shown in FIG. 10( b) is similar to the arrangement in FIG. 10( a) except that base element 14 a′ of concentrator 14′ is a solid cylindrical disk. The arrangement shown in FIG. 10( c) is similar to the arrangement shown in FIG. 10( b) except that offset element 14 e″ of concentrator 14″ is a solid cylindrical disk.

FIG. 11( a) and FIG. 11( b) illustrate examples of the present invention particularly suitable for use with low resistivity tubular material. In these examples, the end of tube flux concentrator comprises fixed annulus 15, as shown in FIG. 11( a), or adjustable iris diaphragm 15′, as shown in FIG. 11( b), which effectively functions as an annulus with a variable opening to accommodate induction heating of tubular materials with different properties and physical characteristics. FIG. 11( b) shows a typical, but non-limiting, example of an adjustable iris diaphragm wherein blades 15′a are rotationally attached to mounting structure 15′b so that rotation of the blades results in increasing or decreasing the size of opening 15′c. The central axes of both annulus 15 and diaphragm 15′ can be aligned with the central axis of either the induction coil or the tube within the induction coil. An overhang distance, as illustrated in FIG. 11( a), may be provided when either the annulus or diaphragm is used, or the end of the tube may be in contact with the surface of the annulus or diaphragm. The fixed radius of the annulus 15, or variable radius of diaphragm 15′, can range from less than the inner diameter of the tubular material to the inner dimension (e.g. diameter) of the induction coil.

When a central pole element is used in other examples of the invention, the central pole element may comprise a plurality of structures that collectively form a central pole element to establish a particular flux path around the central axis of the tubular material. For example, in FIG. 12, magnetic flux concentrator 20 comprises base 20 a, peripheral poles 20 b and central pole 20 c, wherein central pole 20 c comprises four wedge elements 20 c′ arranged symmetrically around a central axis. Each wedge element 20 c′ has a base leg element 20 a′ extending substantially perpendicular from one end (referred to as the converging end) of the wedge element to collectively form base 20 a. Peripheral pole 20 b extends from the opposing end (referred to as the diverging end) of each edge element as shown in FIG. 12 and FIG. 16( a). In other examples of the invention the number of peripheral poles may be increased, for example, to four or six, as shown in FIG. 16( b) and FIG. 16( c), respectively, or any other number of poles.

FIG. 13( a) and FIG. 13( b) illustrate examples of concentrator 20 wherein two peripheral poles 20 b are used. The arrangement and configuration is similar to that in FIG. 4( a) and FIG. 4( b), respectively, except that in FIG. 4( a) and FIG. 4( b) a cylindrical base 10 a and central pole 10 c are used. In FIG. 13( a) the end of central pole 20 c (comprising two wedge elements 20 c′) is positioned about the X-axis in the interior opening of the tubular element 95 p for a distance x₁ to achieve required end heated length 92; whereas in FIG. 13( b) central pole 20 c of concentrator 20 is positioned along the X-axis into the interior opening of tubular element 95 q for a distance x₂ to achieve required end heated length 92. Depending upon specific requirements of an application, the distance x₂ could be negative; that is, end 202 c _(end) of the central pole 20 c can be located at a certain distance outside of the tube in the coil overhang region.

FIG. 14( a) and FIG. 14( b) illustrate examples of concentrator 21 wherein peripheral poles 21 b and optional leg elements 21 d are fixed, while base element 21 a (comprising two base leg elements 21 a′) and the central pole 21 c (comprising two wedge elements 21 c′) can be moved in the +X and −X directions. The arrangement and configuration is similar to that in FIG. 5( a) and FIG. 5( b), respectively, except that in FIG. 5( a) and FIG. 5( b) a cylindrical base 11 a and central pole 11 c are used, and only the central pole is moveable. As illustrated in FIG. 14( a), the end of central pole 21 c is positioned along the X-axis into the interior opening of tubular element 95 r for a distance of x₃ to achieve required end heated length 92; whereas in FIG. 14( b), central pole 21 c of concentrator 21 is positioned along the X-axis into the interior opening of tubular element 95 s for a distance x₄ to achieve required end heated length 92.

FIG. 15( a) and FIG. 15( b) illustrate examples of concentrator 25 wherein peripheral poles 25 b are fixed while leg elements 25 d are moveable in a direction generally parallel to the length of its adjacent peripheral pole. The arrangement and configuration is similar to that in FIG. 6( a) and FIG. 6( b), respectively, except that in FIG. 6( a) and FIG. 6( b) a cylindrical base 11 a and central pole 11 c are used. As illustrated in FIG. 15( a), leg element 25 d is positioned along peripheral pole element 25 b at a distance of x′₅ from the extend end of the peripheral pole element to achieve required end heated length 92; whereas in FIG. 15( b), leg element 25 d is positioned at x′₀, which is defined as the location of the extended end of the peripheral pole element. In other examples of the invention, a combination of movement of leg elements 25 d, and base element 25 a (comprising two base leg elements 25 a′) and the central pole 25 c (comprising two wedge elements 25 c′), as described above, may be used.

In other examples of the invention, radial movement of selected components of the magnetic flux concentrator about the central axis of the tubular material can be accomplished, with or without movement of one or more of the concentrator's components along the X-axis. Suitable mechanical elements may be used to provide the radial movement. By way of example and not limitation, FIG. 17( a), FIG. 17( b) and FIG. 17( c) illustrate one example of the present invention wherein selected components of the magnetic flux concentrator are moved radially about the central (longitudinal) axis of the tubular material. Such movement may be useful in accommodating tubular material of different diameters as further described below. Referring to these figures, the exemplary magnetic flux concentrator 22 is similar to concentrator 20 illustrated in FIG. 13( a) and FIG. 13( b) except for the following changes. There are six peripheral poles 22 b that are located around induction coil 30, along with optional leg elements 22 d. Each base leg element 22 a′ and wedge element 22 c′ are radially moveable about central axis A-A′ of the tubular material. The six base leg elements are attached to structural support element 44 via cam pins 46 through slots in cam follower 40 and cam plate 42 (47 and 45 respectively). Cam plate 42 is free to rotate between structural support element 44 and cam follower 40 whereby cam pins 46 slide each base leg element 22 a′ and wedge element 22 c′ either towards or away from the central axis. FIG. 18( a), FIG. 18( b) and FIG. 18( c) illustrate the effect of rotating cam shaft 42 by actuator arm 48 in the counterclockwise direction progressing from FIG. 18( a) to FIG. 18( c). As the tubular material decreases in diameter from tube 95 x in FIG. 18( a) to tube 95 z in FIG. 18( c), wedge elements 22 c′ and base leg elements 22 a′ move radially towards the central axis so that the wedge elements can still be inserted within the interior of the tubular material with minimal radial gap as the inside diameter of the tubular material decreases.

Any of the flux concentrators of the present invention may be combined with a variable winding induction coil wherein the induction coil has a tighter turn ratio (number of turns per unit length, L) around the thermal transition zone 94 than in the end heated length 92 as illustrated in FIG. 19.

Features of the magnetic flux concentrator of the present invention illustrated in separate example of the invention may be combined in other examples of the invention. In all examples of the invention, the magnetic flux concentrator may be formed from any suitable material that is magnetically conductive (high permeability) and has relatively high electrical resistivity (low power loss). In form the magnetic flux concentrator may be a laminated stack of magnetic material, ferrite, iron-based and ferrite-based powder materials, and may be cast or assembled in parts.

In all examples of the invention, the term “tubular material” includes pipes and tubes, but also includes any material having a longitudinal (central) axis and an interior opening. For example, the tubular material may be rectangular in cross section and have a corresponding rectangular interior opening; in this example of the invention the central pole may be rectangular in shape for insertion into the rectangular opening in the tubular material.

In all examples of the invention movement of the magnetic flux concentrator may be accomplished by any method, including but not limited to, movement by a human operator, or a linear drive means, such as an electric or hydraulic drive. Further movement may be manually or automatically accomplished in some examples of the invention. For example sensors may sense the dimensions of the tubular material to be presently heat treated, and output a signal to a processor which executes a program for appropriately moving the position of the concentrator. Sensors may be proximity sensors, sensing for example, the position of the exterior and/or interior of the tubular material to be heat treated. In other examples of the invention a human operator may input data to a processor via a suitable input device, such as a keyboard, to identify the tubular material to be heat treated, and the flux concentrator would move according to a stored position value. In other examples of the invention sensors may be used to sense in real time point end heating temperatures, for examples, by pyrometers, infrared sensors or other thermal imaging sensors, to sense real time point end heating, to adaptively adjust the radial and axial position of concentrator. This alternative would account for metallurgical anomalies in a particular size of tubular material and adjust the position of concentrator accordingly.

A single layer, multi-turn coil is shown in the above examples of the invention. However the invention is not limited to a particular type of coil design. For example a single turn coil, multiple layers of coils, or multiple coils connected to a plurality of power sources may be used with the apparatus of the present invention.

Depending on the application and process requirements, different designs of flux concentrators may be used. For example lamination stacks may be a continuous circular element, or can be fabricated from multiple stacks. Depending upon application and specifics of process requirements: a “C”-shaped (base element and two peripheral poles with no central pole); a double “C”-shaped (base element and four peripheral poles with no central pole); a “T”-shaped (base element and central pole with no peripheral poles); or an “I”-shaped lamination or powder formed flux concentrator, or any combination of the above shapes, may be used instead of an “E”-shaped concentrator.

While the above examples of the invention describe keeping the position of the solenoidal coil constant, in other examples of the invention a combination of the movement of the solenoidal coil and end magnetic flux concentrator described in any of the above examples of the invention may be used without deviating from the scope of the invention. In other examples of the invention any of the concentrators and/or tubular material in the above examples of the invention may be rotated during the induction heat treatment process.

The term “solenoidal induction coil” as used in the invention is understood in its broadest sense as any combination of one or more induction coils in which a magnetic field is generated when an ac current flows through the one or more induction coils, and the magnetic field couples with the end of a tubular material inserted into the one or more induction coil. The invention is not limited to a particular geometric configuration of a induction coil.

In all examples of the invention, both ends of a tubular material can be induction heated at the same time by inserting the entire length of the tubular material into a solenoidal induction coil so that an overhang distance is established at both ends of the tubular material.

The above examples of the invention have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the invention has been described with reference to various embodiments, the words used herein are words of description and illustration, rather than words of limitations. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses. Those skilled in the art, having the benefit of the teachings of this specification and the appended claims, may affect numerous modifications thereto, and changes may be made without departing from the scope of the invention in its aspects. The invention is not limited to what is described above but also includes the invention as recited in the attached claims. 

The invention claimed is:
 1. An end of tube flux concentrator for induction heat treatment of an end of a tube inserted within a solenoidal induction coil, the end of tube flux concentrator comprising: a disc base; a plurality of peripheral poles radially distributed around the perimeter of the disc base, each of the plurality of peripheral poles extending generally perpendicularly from a tube-facing side of the disc base to an extended peripheral pole end, the plurality of peripheral poles arranged relative to the tube-facing side of the disc base so that when the disc base is brought into the vicinity of the end of the tube inserted within the solenoidal induction coil the plurality of peripheral poles at least partially surround the exterior of the solenoidal induction coil.
 2. The end of tube flux concentrator of claim 1 wherein the disc base is a solid cylindrical disc.
 3. The end of tube flux concentrator of claim 1 wherein the plurality of peripheral poles form a substantially solid cylindrical peripheral pole structure around the disc base.
 4. The end of tube flux concentrator of claim 1 further comprising a base offset element extending from the tube-facing surface of the base.
 5. The end of tube flux concentrator of claim 1 further comprising at least one central pole extending generally from the central region of the tube-facing side of the disc base, the at least one central pole arranged relative to the tube-facing side of the disc base so that when the disc base is brought into the vicinity of the end of the tube inserted into the solenoidal induction coil the at least one central pole extends at least partially into the end of the tube.
 6. The end of tube flux concentrator of claim 5 wherein the at least one central pole is cylindrically or conically shaped.
 7. The end of tube flux concentrator of claim 5 wherein the at least one central pole is moveable along its axial length relative to the base.
 8. The end of tube flux concentrator of claim 7 wherein the at least one central pole is cylindrically or conically shaped.
 9. The end of tube flux concentrator of claim 1 wherein the base is moveable along its axial length relative to the plurality of peripheral poles.
 10. The end of tube flux concentrator of claim 1 further comprising a flux concentrator leg adjacent to the extended peripheral pole end of at least one of the plurality of peripheral poles, the flux concentrator leg oriented towards the longitudinal axis of the end of tube flux concentrator and arranged relative to the extended peripheral pole end so that when the disc base is brought into the vicinity of the end of the tube inserted into the solenoidal induction coil the flux concentrator leg extends beyond the end of the solenoidal induction coil.
 11. The end of tube flux concentrator of claim 10 wherein the flux concentrator leg is moveable in a direction substantially parallel to the at least one of the plurality of peripheral poles.
 12. The end of tube flux concentrator of claim 5 wherein the base is formed from a plurality of base legs radially distributed about the longitudinal axis of the flux concentrator; the at least one central pole comprises a plurality of wedges, each of the plurality of wedges extending generally perpendicularly from the tube-facing side of the converging end of each of the plurality of base legs; and each of the plurality of peripheral poles comprises a peripheral pole extending generally perpendicularly from the tube end-facing side of the diverging end of each of the plurality of base legs.
 13. The end of tube flux concentrator of claim 12 wherein the combination of the base and the at least one central pole is moveable along the longitudinal axis of the flux concentrator relative to the peripheral poles.
 14. The end of tube flux concentrator of claim 12 further comprising a flux concentrator leg adjacent to the extended end of at least one of the plurality of peripheral poles, the flux concentrator leg oriented towards the longitudinal axis of the end of tube flux concentrator.
 15. The end of tube flux concentrator of claim 14 wherein the flux concentrator leg is moveable in a direction substantially parallel to the at least one of the plurality of peripheral poles.
 16. The end of tube flux concentrator of claim 12 wherein the combination of the base and the at least one central pole is moveable in a direction substantially perpendicular to the longitudinal axis of the flux concentrator.
 17. An end of tube flux concentrator comprising a plurality of base legs, each of the plurality of base legs extending from a converging end substantially perpendicular to the longitudinal axis of the flux concentrator; a wedge element extending generally perpendicular from a tube-facing side of the converging end of at least one of the plurality of base legs to collectively form a central pole; a peripheral pole extending generally perpendicular from the tube-facing side of the end of at least one of the plurality of base legs opposite the converging end of the at least one of the plurality of base legs.
 18. The end of tube flux concentrator of claim 17 further comprising a flux concentrator leg adjacent to the extended end of at least one of the peripheral poles.
 19. The end of tube flux concentrator of claim 17 wherein the combination of the plurality of base legs and the central pole is moveable along the central axis of the flux concentrator.
 20. The end of tube flux concentrator of claim 17 wherein the combination of the plurality of base legs and the central pole is moveable in a direction substantially perpendicular to the central axis of the flux concentrator. 